plugins: rename ubuntu provisioning plugins

As the android-provision plugin and related android-apndb
code really is Ubuntu specific, re-name the files from
android-* to ubuntu-*.
build: handled re-named ubuntu provision code
plugins: remove mbpi from ubuntu provisioning

Remove the additional mbpi APN query from the
ubuntu-provision plugin.  Also add support for
an optional custom apn file which may be present
in /custom/etc.
Merge pull request #101 from tonyespy/no-mbpi-add-custom

Merged